#define _CRT_SECURE_NO_WARNINGS 1

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    int getDecimalValue(ListNode* head) {
        int i = 0;
        return change(head, i);
    }
    int change(ListNode* node, int& i)
    {
        if (node->next == nullptr)
        {
            return node->val * pow(2, i++);
        }
        return change(node->next, i) + node->val * pow(2, i++);
    }
};